Blasting cap



D. F. NORTH Aug. 27, 1935.

BLASTING CAP Filed July 29, 1933 W/T/VESS:

Patented Aug. 27, 1935 UNITED STATES PAT E T GFFICE Application `luly`29, 1.933, Serial No. 682.752

5 Claims.

This'invention relates to blasting caps and more particularly to a blasting cap provided with means whereby actual firing through contact of the lead wires with a source of current will be positively avoided.

In order to avoid the accidental ignition of blasting caps adapted for electrical firing, it has been customary to provide means for short circuiting the lead wires until ignition is to take place. The preferred type of short circuiting arrangement involves the use of a bridging member for the uninsulated ends of the lead wires, which bridging member is adapted to be readily removed before tiring takes place. A very satisfactory type of bridging member is shown in the patent to Barab 1,895,438, dated January 3l, 1933. This comprises an eyelet of soft material in a peripheral groove of which the lead Wires are clamped to provide the necessary short-circuit. The present invention is applicable to blasting caps asso-I ciad with short circuiting conducting members of various forms having, however, the characteristic of that disclosed in the Barab patent in that they are readily removed by the application of moderate force. Some short-circuiting members of this type, for example, consist of conductors soldered across the wires or comprise metallic plates having their ends turned inwardly about the wires and clamped thereon the metal being soft and thin so that disengagement may be readily effected when desired, although accidental disengagement is substantially prevented.

One drawback in connection with such short circuiting members is that they are located at" the ends of the relatively'short lead Wires directly connected to the caps. Their removal has accordingly necessitated the presence of a Workman dangerously close to the charge to be red with the possibility that if there happened to be a voltage applied to the ring circuit an immediate explosion might occur as soon as the short circuit is broken.

To avoid this diiiiculty means have been proposed for removing the short circuiting member by manipulation at a safe distance from the blasting cap. One suggestion heretofore made involves the use of a separate cord, or the like, which may be manipulated at a distance. It has also been suggested to connect the short circuiting member with a cord secured to the firing circuit at a distance from the short circuiting member which is greater, when measured along the firing circuit, than the cord itself. A sharp pull on the ring circuit Will in such case dislodge the short circuiting member to prepare the setup for iiring. The use of such auxiliary device, however, is objectionable in that if the auxiliary cord is free the cord may become twisted in the lead wires with the possibility that during unreeling of the wires the short circuiting element will be disconnected. The danger of this is even greater when the cord is attached in any fashion inasmuch as handling of the wires is likely to result in a premature interruption of the short circuit.

It is the object of the present invention to provide an arrangement whereby without the provision of 'any auxiliary means but by a mere arrangement of the lead 'Wires and ring circuit wires provision is made for interrupting the short circuit located a short distance from the blasting l cap.

Both the broad objects of the invention and the specific ones relating to desirable details will become apparent from the following description read in conjunction with the accompanying drawing in which: Figgl illustrates diagrammatically a firing circuit prior to the interruption of the short circuit;

Fig. 2 is a similar view of the same showing the opening of the short circuit and preparation of the circuit for firing; and

Fig. 3 is an enlarged plan View' showing a blasting cap, its associated lead wires and a short circuiting member provided in accordance with the invention.

Referring first to Fig. 3 there is illustrated at 2 a blasting cap of the conventional type provided With an igniter in which is located a filament whose ends are connected to the insulated lead wires 4 and 6 provided lwith uninsulated end portions 8 and I0. The lead wire 6 in the present instance is substantially longer than the lead wire 4 being provided with a portion I2 doubled back on itself as indicated in the ligure. 'Ihe difference in length is such that the insulated length of lead wire 6 is greater than the' total length of the lead wire 4 including its uninsulated portion. There is provided at I4 a short circuiting member of the type illustrated in the Barab patent although it will be understood that this 4short circuit-ingmember may be of any form. adapted .to be released from the wires by the imposition of the type of eiort indicated below. Preferably the uninsulated portion of lead wire 6 indicated at l0 extends beyond the short circuiting member I4 further than the uninsulated portion 8 of the lead wire 4. This merely serves as an indication that the end I0 corresponds to that lead wire which is the longer.

' being or substantially greater length than the There is indicated diagrammatically` at Il a blasting machine of the usual type designed to furnish the current .for ilring the cap. Firing wires Il and 2l are connected to this machine and are electrically secured to the uninsulated ends of the lead wiresy 4 and 4 as indicated at 22 and 26. The-ilring wire Il which is connected to the shorter lead wire 4 is made extray long asv indicated at 24,'its excess length over the ring wire 2l being preferably of the order of the excess length of the lead wire 6 over` the'lead wire 4.

Originally the firing circuit will be as indicated Vin Fig. l. All of the lengths of this figure are: of

course,` considerably shortened, the lead wires being oisubstantial length but not oi.' a length corresponding to a safe distance from the charge, while the il'ring wires are of very considerable =length so that the-blasting machine is at a sate distance. By pulling upon the ilring wires adjacent the blasting'machine, or at any intermediate sale distance, strains will be imparted to the short'circuiting member serving to disengage it from at least one' of the lead wires. Pulling the wires further will serve to bring the uninsulated portions 'of one opposite the insulated portions oi" While any desirable means may be provided tov identifythe longer of the lead wires and also the longer ot the wires of f the iiring.circuit, it is very convenient to make the provision indicated above, namely, that the uninsulated end beyond the short circuiting member of one wire be greater than the corresponding end/ofthe other.

It will be obvious that numerous variations may be made in the embodiment of the invention without departing rrfrom the spirit thereofas defined in the following claims.

Patent is:

l. In combination, a blasting capadapted for electrical ring,4 lead wires from the cap having uninsulated end portions, and a removable con- "ducting member connecting the uninsulated end portions of the lead wires, one of said lead wires other between the cap and the conducting member, the difference in length being greater than the uninsulated portion oifthe shorter wire.

2. In combination, a blasting cap adapted for electrical ilring. lead wires from the cap having ,uninsulated end portions, and a removable conducting member connecting the uninsulated end portions of the lead wires, one oiy saidl lead wires being of substantially greater length than the the shorter wire. v f

3. In combination, a blasting cap adapted for electrical iiring, lead wires from the cap having 'uninsulated end portions, and a removable conmember connecting. the uninsulated end por tions of the lead wires, one of said lead wires being ot ysubstantially greater length than .the other between the cap and conducting member, whereby slack is provided in the wire of greater length between the cap and the conducting member, a current generator, and ilring wires extend-Y ing from the generator and having uninsulated end portions connected to the unlnsulated end portions of the lead wires, the tiring wire connected to the shorter lead wire being longer than the other whereby slack is provided in the longer wire between the generator and the conducting member.

5. In combination, av blasting cap adapted for electricaliiring, lead wires from the cap having uninsulated end portions, and a removable conducting member connecting the uninsulated end portions of the lead wires, one of said' lead wires being oi.' substantially greater length than the What lI claim and desire to protect by Lettersy other between the cap and the conducting member,..and the end portion oi' one lead wire beyond the conducting member being longer than the corresponding end portion of the other, the insulated'portion ot the-longer lead wire being o! .greater length than the total length 01' the Shorter other between the cap and the conducting niem- ,1-

ber, the insulated portion of the. longer wire being of greater length than the total extent otvr 

